Semiconductor devices in the form of integrated circuits are used in virtually all electronic devices. A typical integrated circuit includes a die formed of silicon with transistors and other active and passive devices formed on the silicon. The integrated circuit die is typically included in an integrated circuit package. The package typically provides for the die: electrical interconnection, mechanical support, heat dissipation, and protection.
Most integrated circuit packages include a leadframe which carries the external connection pins, wire bonds between the leadframe and the die, and an encapsulant. The encapsulant is typically a plastic which is molded around the other components and cured during manufacturing to thereby protect the encapsulated components from the ambient environment. Ceramics are used in some applications as the encapsulating material, but are more expensive and require higher energy processing as compared to plastics.
Thermosetting epoxy materials are typically used for plastic packages. These materials are typically made with fused silica as a filler, such as greater than 60% by weight. The epoxy may include cresylic novolac resin and phenolic novolac resin as the hardener. In addition, a flame retardant, such as antimony trioxide or bromine is included. The thermosetting epoxy is permanently cured, typically by the application of heat, during the molding process.
It is often desirable to non-destructively access the integrated circuit die after the packaging has been completed. For example, if device testing indicates that the integrated circuit is defective, it is often desirable to perform an analysis to determine what caused the failure. The results of the failure analysis may be useful to change one or more manufacturing techniques to thereby reduce the number of future defects.
Unfortunately, removal of the encapsulant material from the integrated circuit is not a simple process. The thermosetting encapsulants typically used will not simply reflow upon the application of heat thereby exposing the underlying leadframe, bond wires and circuit die. It is typically important for subsequent testing that the die and bonding system not be destroyed, and that electrical connections can be established to facilitate electrical performance testing.
One conventional approach to removing the encapsulant or "decapsulating" an integrated circuit etches the encapsulant by applying concentrated acids, such as fuming nitric and fuming sulphuric acid or certain organic solvents, to the encapsulant. There are, of course difficulties with controlling the desired amount of etching, preventing damage to the interior metal components, and removing debris during the etching. Some of these difficulties are addressed, for example, in U.S. Pat. No. 5,766,496 to Martin which discloses an apparatus and associated method using an acid etch and wherein a first syringe pump pumps etchant into an etch head, and a second syringe pump agitates the first quantity of etching repeatedly into and out of an etched cavity. The etch head also includes a heater to heat the volume of etchant prior to its introduction against the encapsulant. Unfortunately, the apparatus and method still rely on the precise delivery and control of acid etchants.
U.S. Pat. No. 4,344,809 to Wensink discloses a jet etch apparatus for decapsulating the molded resin material from an integrated circuit device. The apparatus includes a jet pump or aspirator connected by a tube to an etching block. the etching block is further connected by a tube to a container for holding an etchant solution. The integrated circuit is placed on top of the etching block and as fluid flows through the jet pump, a suction is created drawing etching solution through the etching block and a hole is etched in the encapsulating material. The etchant solution is fuming sulphuric acid. U.S. Pat. No. 4,359,360 also discloses an approach using a heated etchant solution to jet etch the encapsulating material from an integrated circuit. Along these lines, U.S. Pat. No. 4,826,556 further includes a shield for shielding the integrated circuit from outside air to maintain pressure of the etchant fed by an etchant feed pump.
The hot acid etching decapsulating techniques may take from several minutes up to hours to remove the encapsulant. The acid etchant materials raise handling and disposal concerns. Controllability of the etching is also difficult and may result in destruction of the upper surface portions of the die and/or the bond pads. In addition, any ionic contamination at the surface of the die, as may be the cause of certain failures, would be typically be removed during acid etching.
Yet another conventional decapsulating technique includes exposing the integrated circuit to an oxygen plasma. Unfortunately, this approach may take several hours or even several days. In addition, the oxygen plasma etching equipment is relatively expensive.